Within the field of watchmaking, a striking mechanism can be combined with a conventional watch movement to act as a minute repeater or to indicate a programmed alarm time. This type of striking mechanism generally includes at least one gong made of metallic material, such as steel, bronze, precious metal, metallic glass, sapphire or quartz. The gong may describe, for example, at least one portion of a circle around the watch movement inside the watch frame. The gong is secured by at least one end thereof to a gong-carrier, which is in turn secured to a watch plate. A strike-hammer is rotatably mounted on the plate, for example, in proximity to the gong-carrier so as to strike the gong and cause it to vibrate. The sound produced when the gong is struck by the hammer is within the audible frequency range of 1 kHz to 20 kHz. This indicates a well defined time, a programmed alarm or a minute repeater to the person wearing the watch.
As shown in EP Patent No 1 574 917, the striking mechanism of a watch may include two gongs each secured via one end thereof to the same gong-carrier, which is in turn secured to a plate. Each gong may be struck by a respective hammer. To achieve this, each hammer is driven by its own drive spring, which must have been pre-wound, so as to drive the hammer against the gong to indicate a minute repeater or an alarm time. Two damper counter-springs are each provided to push back and hold the two hammers away from the gongs in an idle mode. The damper counter-springs also slow down the fall of each hammer before it strikes the respective gong and then push the hammer back into the idle position. Eccentrics are also provided for adjusting the operation of the counter-springs to prevent each hammer from rebounding against the respective gong.
One drawback of this type of striking mechanism structure with counter-springs is that there is a significant loss of kinetic energy when the hammer strikes the respective gong, which reduces the acoustic level of the striking work. This energy loss is largely due to the slowing down imposed by each counter-spring on the path of the hammer when it strikes the gong. Moreover, even if the pre-winding of the drive springs is increased, this involves adapting the counter-springs via their eccentric, also to prevent any rebound, which is another drawback of this type of striking mechanism.
EP Patent No. 2 048 548, which mainly discloses a hammer of a watch striking mechanism may also be cited. This hammer includes two parts hinged to each other and a resilient member secured to one of the hinged parts. When the hammer is in a stable position, the resilient spring member holds the two parts of the hammer, whereas when the hammer is in the striking position, the two parts move away from each other, returned by the resilient spring member. With this arrangement, it is possible to reduce the kinetic energy that the hammer loses against a damper member. However, this type of hammer arrangement complicates the fabrication of the striking mechanism to prevent the hammer losing energy when it strikes the gong, which is a drawback. Undesirable rebounds of the hammer against the gong may also occur during the strike, which is another drawback.